A patent application, entitled "Wafer Retaining Mechanism," filed by the same Applicant on Dec. 19, 1997, App. Ser. No. 08/994,982, now U.S. Pat. No. 5,890,597, relates to a wafer retaining mechanism comprising a link mechanism disposed at inside of a canopy for retaining and locating wafers. The link mechanism includes a base rod affixed to the canopy, a sliding rod movable within the base rod, a front link, and an upper and lower links pivoted on the sliding rod and the front link. When the canopy receives a wafer cassette, the sliding rod of the retaining mechanism urges against a chassis located at bottom of the wafer cassette subjecting the sliding rod to move upwards within the base rod for urging the lower link outwards, such that lower end of the front link is urged obliquely outwards in response to the action of the lower link. The upper link is activated to push the upper end of the front link by external forces when the sliding rod and the front link both urge against the chassis. The wafers are then urged to align in place when all links of the retaining mechanism are expanded.
The present invention is substantially similar to the structure of the above-mentioned application in respect to the wafer retaining mechanism. The features that distinguish the present invention from said application reside in that the link unit is featured with engaging sections at respective pivots, which the engaging sections, in response to proper external forces, engage or disengage components of the link unit so as to facilitate assembly or disassembly of the link unit.